Various types of wireless communication services using mobile communication terminals are being developed in line with the remarkable development of electronic and communication technologies. Conventional services include wireless voice communication services providing mobile communication terminal users with wireless voice communication regardless of time and space, and text message services supplementing the voice communication services.
Wireless Internet services have recently commenced, which provide mobile communication service subscribers with Internet communication services via wireless communication networks, in line with the developing wireless Internet, and various technologies are being developed in connection with the wireless Internet.
Among various wireless Internet services using mobile communication terminals, the LBS (Location-Based Service) is recently drawing much attention due to the wide range of usefulness and convenience. The LBS refers to a communication service for positioning a mobile communication terminal and providing additional information based on the positioning result. The LBS is used in various fields and circumstances, including emergency aid requests, responses to crime reports, GIS (Geographical Information System) for providing information regarding adjacent regions, differentiation of mobile communication fees based on location, traffic information, vehicle navigation, circulation control, location-based CRM (Customer Relationship Management), etc.
Location measurement schemes for providing mobile communication terminals with the LBS include network-based schemes relying on the propagation environment (i.e. cell radius of a base station in a mobile communication network) to measure the location of mobile communication terminals and confirm the location on a software basis, handset-based schemes using GPS (Global Positioning System) receivers mounted in mobile communication terminals, and hybrid schemes combining both schemes.
The A-GPS scheme is one of the handset-based schemes, and is compatible with both European GSM (Global System for Mobile Communication)-based networks using the TDMA (Time Division Multiple Access) wireless access scheme and IS-95-based networks using the CDMA (Code Division Multiple Access) wireless access scheme. According to the GSM wireless scheme, mobile communication terminals are positioned by transmitting/receiving messages through an OMA SUPL (Secure User Plane Location) interface between the mobile communication terminals incorporating GPS receivers and the SPC (SUPL Positioning Center) within the GSM network and through an SUPL POS for A-GPS location measurement within the OMA SUPL (i.e. GSM A-PGS protocol incorporating an RRLP (Radio Resource Location Protocol)). This type of positioning is very accurate because satellite signals are received from at least four GPS satellites to measure the location. The A-GPS system includes an SPC for receiving satellite signals received by mobile communication terminals and calculating the location, and an SLC (SUPL Location Center) for processing the calculation based on information regarding base stations within the GSM mobile communication network or associating the information with other systems.
The E-OTD (Enhanced Observed Time Difference) scheme is a representative network-based location measurement scheme, and has been standardized through LCS Release 98 and 99 by the GSM standardization committee of the European TDMA-based GSM scheme using the TDMA wireless access standard. According to the E-OTD, signals received from at least three base stations by a mobile communication terminal are used to calculate the difference in time of arrival and distance and determine the location. In other words, the E-OTD scheme combines various time difference concepts, including OTD (Observed Time Difference), RTD (Relative Time Difference), GTD (Geometric Time Difference), etc. for network-type location calculation.
The OTD refers to the difference in time spent by signals from two base stations to reach a mobile communication terminal, and can be obtained by measuring the UE Rx-Tx time difference type 2 parameter by a GSM-based mobile communication terminal.
The RTD refers to a parameter used to obtain the difference in starting time of signals transmitted by two base stations, and can only be measured by equipping the base stations with a separate measuring device, i.e. LMU (Location Measurement Unit). This means that, in order to obtain the key parameter necessary for network-type location calculation recommended by the GSM standard, i.e. “GTD=OTD-RTD”, not only the OTD, but also the RTD must be obtained for the E-OTD-type network location calculation.
According to network-based location measurement technology, data (PPM, OTD, RTD, etc.) measured by a mobile communication terminal and an LMU is transmitted to a location measurement server according to a protocol (IS-801, RRLP, RRC, etc.) agreed upon between the mobile communication terminal and the server, and the data (PPM, OTD, RTD, etc.) measured by the mobile communication terminal is used by the location measurement server to measure the location of the corresponding mobile communication terminal. The location measurement server conducts network-type location measurement (i.e. the server side measures the location of the terminal that has requested location measurement, location measurement schemes using GPS satellites being excluded), and transmits the result to the requesting party (SLC, CP (Contents Provider), mobile communication terminal that has requested the service, etc).
The network-based location measurement technology includes a cell ID scheme using the base station radius cell, an AOA (Angle of Arrival) scheme according to which the base station receives signals from a mobile communication terminal and calculates the LOB (Line of Bearing) to calculate the location, a TOM (Time of Arrival) scheme according to which the location of a mobile communication terminal is calculated based on the time of arrival of radio waves from at least three base stations, and a TDOA (Time Difference of Arrival) scheme according to which the difference in time of arrival of pilot signals received by a mobile communication terminal from three base stations is measured to calculate the difference in distance between the base stations so that the point of intersection of two resulting hyperbolas is determined as the location of the mobile communication terminal.
However, the above-mentioned conventional network-based location measurement schemes have the following problems.
Firstly, when data regarding parameters (i.e. time and distance) measured by a mobile communication terminal or the mobile communication network is used for triangulation or to calculate the point of intersection of hyperbolas, repeaters heavily affect the result. This means that, if repeaters are used, data measured by a mobile communication terminal regarding the time and distance between the base station and the mobile communication terminal is delayed relative to the original data. This degrades the location measurement accuracy.
Secondly, in the case of triangulation using time and distance measurement parameters in an asynchronous mobile communication network (GSM or W-CDMA), not only the OTD measured by a mobile communication terminal, but also the RTD value measured by an additional LMU equipped with separate GPS equipment must be measured to obtain the location measurement result from the formula. Considering that it has little merit per investment to additionally install LMUs in the entire mobile communication network for the network-type location measurement, triangulation-based network location measurement cannot be used in a region having no LMU installed therein.
Thirdly, when a base station is rearranged, the latitude and longitude data of the rearranged base station is not instantly reflected. This means that there is no confirming whether or not the latitude and longitude data referred to for location measurement is identical to the latitude and longitude data of the rearranged base station.
Fourthly, since each network-based location measurement technology has different characteristics regarding the mobile communication base stations and sectors, excessive human and material resources are used to optimize parameters, which are differently used by base stations or sectors, for the purpose of improving the location measurement accuracy. This slows down the commercialization.